In a recent report to federal highway officials, the city said the number of right hook crashes (where a vehicle turns right into a bicyclist) doubled from 16 to 32 over a four-year period. Officials also noted that more cyclists are on the roads now than in 2008 when the boxes were installed, which they said could be a reason for the increased number of crashes.

The crashes were more common at downhill bike boxes, where bicyclists pick up speed before coming to an intersection.

During the four year period from 2008 to 2011, 26 of the 32 right hook crashes (81 percent) occurred at four intersections containing bike boxes, according to the report:

SW Madision and 3rd Avenue

SE Hawthorne and 7th Avenue

SE Hawthorne and 11th Avenue

NW Everett Street and 16th Avenue

All four locations have a downhill approach, the report said.

PBOT officials are recommending additional striping leading up those bike boxes on slopes and lettering in the bike lanes warning bicyclists to look for vehicles making right turns.

They also recommend more street lights to improve visibility and new green markings in the intersections.

"In the downhill sections, you know, I think encouraging people to be extra cautious is a good idea," said Gerik Kransky with the Bicycle Transportation Alliance. "They're seeing a unique concern and they're treating it with some new ideas."

The new recommendations follow a deadly collision in May, when Kathryn Rickson was riding downhill and was hit by a truck turning right at Southwest Madison and 3rd Avenue.

“These improvements will help make our bike facilities safer and remind all road users to be alert when approaching these intersections,” said Portland Mayor Sam Adams in a news release on his website.

“With more and more Portlanders using bicycles as their mode of transportation, making sure that cyclists are more visible to motorists and aware of the right-turning vehicles are important steps that will ultimately save lives.”

The mayor’s office is taking public comments and recommendations for bike box improvements.